In plunger-operated pipettes, the tip element is usually provided with a replaceable tip container or a tip used for drawing therein a liquid to be subsequently dispensed. Usually, pipettes also include a tip remover, comprising a collar slidable along the tip element, and a spring against whose force the collar is pressable downwards. Electrically operated pipettes have also been available, in which the plunger is operated by means of an electric motor. Even in such pipettes, the tip remover has usually been manually operated.
Publication U.S. Pat. No. 4,399,712 discloses an electrically operated pipette, in which the tip remover is powered by the same motor as the plunger. In that configuration, the plunger is provided with two nuts, which are non-rotatable relative to the housing and fitted on motor-driven lead screws. When it is time to remove the tip, the plunger is driven to its bottom position, the nuts pressing a spring-loaded tip removing collar downwards. When the tip is removed, the motor is driven respectively in reverse.